Caring for a mature lilac tree in Victoria, BC, to ensure it flourishes involves attention to a few key areas of maintenance and environmental management. Since mature lilacs are already established, your focus should be on maintaining their health, encouraging blooming, and preventing any issues that could hinder their performance. Here’s what your mature lilac tree needs:

1. Sunlight: Ensure your lilac receives at least 6 hours of direct sunlight daily. Sunlight is crucial for flower production. If surrounding trees or structures shade your lilac, consider pruning them back to increase sun exposure.
2. Soil and Water Management: While mature lilacs are relatively drought-tolerant, they still benefit from consistent moisture, especially in dry periods. Water deeply and infrequently to encourage deep root growth. Ensure the soil around your lilac drains well to prevent root rot. Mulching can help retain soil moisture and regulate soil temperature, but keep mulch away from the stem to avoid moisture buildup that can lead to decay.
3. Pruning: Pruning is essential for maintaining the health and vigor of your lilac. Prune immediately after the blooming period, usually in early summer, to remove spent blooms and thin out dense growth. This encourages light and air circulation, which are critical for reducing disease risk and promoting new growth and blooms for the following year. Remove any dead or diseased wood and thin out the center of the plant to allow sunlight to reach the interior branches.
4. Nutrition: Mature lilacs do not require heavy fertilization, but an application of a balanced, slow-release fertilizer in early spring can support healthy growth and blooming. Avoid high-nitrogen fertilizers, as they can promote foliage growth at the expense of flowers. If your soil is very acidic, consider applying garden lime to adjust the pH closer to neutral or slightly alkaline, which is ideal for lilacs.
5. Pest and Disease Management: Keep an eye out for signs of pests and diseases, such as powdery mildew, lilac borers, or scale insects. Early detection and treatment are key to preventing these issues from impacting the health and blooming of your lilac. Practices like proper pruning and avoiding overhead watering can significantly reduce disease risk.
6. Soil pH and Quality: Lilacs prefer neutral to slightly alkaline soil. If your soil is too acidic, the plant may struggle to absorb nutrients efficiently. Testing your soil’s pH and adjusting it with lime if it’s too acidic can make a big difference in your lilac's health. Incorporating organic matter into the soil can also improve soil structure and fertility, benefiting your lilac.

By following these guidelines, you can help your mature lilac tree thrive in Victoria, BC, enjoying its beautiful blooms and sweet fragrance for many seasons to come.